The theme of the National Religious Broadcasters' convention here this week was "Christian Communicators Pressing Toward the Mark."

For many of the fundamentalist and evangelical Protestants attending the meeting, the "mark" they seemed to have their eye on was a political one. Substantial portions of the convention program involved political muscle-flexing as participants celebrated the victory of their man in last November's election and began planning for the future.

Sen. Jesse Helms (R-N.C.) laid out the agenda for them in the closing hours of the four-day convention.

Like the nation's founding fathers, he said, Americans today are "getting down on their knees for guidance . . . . Millions who never before did it are doing it today." Because of this religious revival, he continued, "God is ready to bless America beyond anything ever seen before."

Linking what he perceived as a return to religion to President Reagan's victory at the polls last November, Helms continued, "It is essential we not lay aside the political aspects of this country's revival. Reagan's success "against such tremendous odds proves America is a God-fearing people . . . . That success will not be lost on future politicians."

John Conlan, a former congressman from Arizona who heads a conservative political activist group called FaithAmerica Foundation, went even further in predicting that "an active and informed voting bloc of 40 million" conservative Christians "will be instrumental in electing the next president of the United States."

Conlan maintained that Reagan got "81 percent of the white, born-again Christian vote" last year. And 8 million or 9 million will be added to that by 1988 through voter registration drives, he said.

"No decision on a candidate has been made yet among major Christian leaders as to which way they will encourage their people to go. That won't be made until 1987," he said.

Who were those would-be king makers? "Certain opinion makers," he responded. No he wouldn't name them. "That wouldn't be wise."

Conlan said that in 1979, "Falwell liked John Conlan" as a presidential candidate "when most of the others went with Reagan . . . . I'm sure that Jerry will move in '87 with Christian leaders as a whole."

After serving four years in the House of Representatives, Conlan lost the Arizona Republican nomination for the Senate in 1976 in a particularly bitter match during which he told voters that "a vote for Conlan is a vote for Christianity." His opponent was Jewish.

His FaithAmerica Foundation produced voter registration and other material for Christian radio and TV stations last year.

He said black Christians failed to support Reagan at the polls last fall because "they didn't know Mondale was antireligious," citing what he termed the Democratic nominee's support of pornography, homosexual rights and his proabortion stance.

Reagan himself put his political agenda before the broadcasters on the first day of their meeting. "You have fought the good fight, for prayer in the schools and against abortion and for freedom in the world," he told the cheering, applauding crowd.

And he asked the broadcasters' continued support for his economic program, to keep the "cost of government . . . from taking the money you deserve to keep for your family and the future" and for "a strong defense."

Following Reagan, singer Pat Boone told the broadcasters, "We are in a spiritual war. There is no Switzerland."

Abortion, pornography and prayer in schools were the issues most prevalent during the sessions. Helms called abortion "our overriding problem . . . when the Supreme Court changed abortion from a crime to a would-be constitutional right . . . . God is not likely to bless this country until we protect the most innocent of human creation."

Helms added "the tyranny known as communism" to the list of evils besetting the country. "The president is right in his perception of the peril facing this nation and the world," he said. "He deserves better than the steady drumbeat against him" by the media.

In the session addressed by Helms, participants found on their seats reprints of articles describing the senator's proposal for conservatives to buy a controlling interest in the CBS network.

Speaking of that idea, he said, "Our goal is not to convert that TV network into a propaganda medium" for conservatives. Rather, he said, the objective is "to have at least one of the networks that would tell the truth . . . with fairness and objectivity."